Many lubricants require extreme pressure additives that are based on sulfur compounds. At high contact pressures the metal being worked heats at its surface and reacts with the sulfur forming metallic sulfides which assist in preventing galling and welding of the metal being worked and the metal working tool such as a lathe, drill, punch, saw, nail machine, screw machine, and similar tools. Currently available sulfurized lubricant additives are either not soluble in water and must be formulated as an emulsion or are ionic in nature and form scums in hard water. Examples of these include sulfurized mineral oils, sulfurized unsaturated fats or fatty acids, some synthetic organic sulfur containing compounds, inorganic polysulfides and sulfur bearing salts. Emulsions often do not have great stability; they are liable to attack by bacteria and they leave residues. A further disadvantage is that because of the emulsifier content of the emulsion the lubricating oils on the moving parts of the machine tool may be dragged into the cutting fluid in emulsified form leading to a deterioration of machine performance. A still further disadvantage of emulsions is that they may present a disposal problem when they are discarded. Many times the emulsions must be purposely broken and the oil and water phases disposed of separately to comply with environmental regulations.
Currently used ionic sulfur bearing salts such as salts of mercaptobenzothiazole have the disadvantages of precipitating with heavy metal ions present in ordinary tap water or resulting from oxidation of the metal piece being worked. Because of this, they must be formulated with chelating agents which may accelerate the corrosion of the work piece and machine. Because of its great water solubility, the diethanol disulfide of my invention overcomes the problems associated with emulsions and ionic sulfur bearing salts.
The metalworking fluids of my invention are brought into contact with the metalwork piece by spraying the fluid or by direction a stream of the fluid on the work piece or by immersion of the work piece in the fluid in a manner such that the work piece, metalworking tool and metalworking fluid are all in intimate contact.